Transcript Electricity and Magnetism

Electricity and
Magnetism
Warm-Up 2/25/2013
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Draw an atom and label all of the parts.
Give an example of static electricity.
What are the three parts of a circuit?
Draw a diagram (using correct symbols) of
a closed circuit – with a switch.
• Draw a diagram (using correct symbols) of
a parallel circuit with 3 light bulbs.
• What are the three types of magnets?
What is electricity?
The collection or flow of
electrons in the form of
an electric charge
What is static electricity?
When two objects rub against each other, electrons
transfer and build up on an object causing it to have a
different charge from its surroundings.
Like the shoes rubbing against the carpet. Electrons are
transferred from the carpet to the shoes.
As electrons collect on an object, it becomes negatively
charged. As electrons leave an object it attains a positive
charges. Charges interact with each other:
Often when you remove clothes
from the clothes dryer, they seem
to stick together. This is because
some of the clothes have gained
electrons by rubbing against
other clothes. The clothes losing
electrons become positive. The
negative clothes are attracted to
the positive clothes.
Have you everrubbed a balloon on your hair and
stuck it on a wall? How do you think this works?
What causes you to be shocked when you rub your feet
across carpet?
An electrical discharge is the passing of an electric
current through the air from a negatively charged object
to a positively charge object. This is what causes
lightning!
Check out these static electricity video clips
•Static electricity at a gas station
•Van de Graaf Generator’s effect on human hair
•Static on Baby’s hair
•Kid gets static going down a slide
•“Cat abuse” by static electricity
What is a conductor and insulator?
A conductor is a material which allows an electric current
to pass. Metals are good conductors of electricity.
An insulator is a material which does not allow an
electric current to pass. Nonmetals are good conductors
of electricity. Plastic, glass, wood, and rubber are good
insulators
How are static charges detected?
What is the difference between static
electricity and current electricity?
Static electricity is stationary or collects on the surface of
an object, whereas current electricity is flowing very
rapidly through a conductor.
The flow of electricity in current electricity has electrical
pressure or voltage. Electric charges flow from an area
of high voltage to an area of low voltage.
Water pressure
and voltage
behave in
similar ways.
• Voltage is a measure
of electrical push!
• The greater the
voltage the greater
the current!
The pressure of the water flowing through the
pipes on the last slide compare to the voltage
(electric potential) flowing through the wires of the
circuit. The unit used to measure voltage is volts
(V).
The flow of charges in a circuit is called current.
Current (I) is measured in Amperes (A).
What are batteries?
Batteries are composed of a chemical substance which
can generate voltage which can be used in a circuit.
There are two kinds of batteries: dry cell and wet cell
batteries. Below is an example of a dry cell.
The zinc container of the
dry cell
contains a moist chemical
paste surrounding a carbon
rod suspended in the
middle.
Wet cell batteries are most commonly
associated with automobile batteries.
A wet cell contains two
connected plates made of
different metals or metal
compounds in a
conducting solution. Most
car batteries have a series
of six cells, each
containing lead and lead
oxide in a sulfuric acid
solution.
What is electrical resistance?
Resistance is the opposition to the flow of an
electric current.
The metal which makes up a
light bulb filament or stovetop
eye has a high electrical
resistance. This causes light
and heat to be given off.
The unit for measuring resistance is the
ohm (Ω).
A thick wire has
less resistance
than a thin wire
and a short wire
has less
resistance than
a long wire.
What are electric circuits?
Circuits typically contain a voltage source, a wire
conductor, and one or more devices which use the
electrical energy.
What is a series circuit?
A series circuit is one which provides a single pathway
for the current to flow. If the circuit breaks, all devices
using the circuit will fail.
What is a parallel circuit?
A parallel circuit has multiple pathways for the current to
flow. If the circuit is broken the current may pass through
other pathways and other devices will continue to work.
What is the difference between an open circuit and a
closed circuit?
A closed circuit is one in which the pathway of the electrical
current is complete and unbroken.
An open circuit is one in which the pathway of the electrical
current is broken. A switch is a device in the circuit in which the
circuit can be closed (turned on) or open (turned off).
How is household wiring arranged?
Most household wiring is logically designed with a
combination of parallel circuits. Electrical energy enters
the home usually at a breaker box or fuse box and
distributes the electricity through multiple circuits. A
breaker box or fuse box is a safety feature.
What is magnetism?
1. Magnetism: -properties and interactions of
magnets
2. Magnets are objects attracted to iron or any material
containing iron.
3. There are three types of magnets: permanent
magnets, temporary magnets, and electromagnets.
4. Magnetic Poles: magnets have two ends or
poles, called north and south poles. At the poles of a
magnet, the magnetic field lines are closer together.
Like poles of magnets repel!
N repels N, S repels S
Unlike poles of magnets attract!
N attracts S
5. Magnetic Field: the area around a
magnet that has a magnetic force. The shape
of the field can be shown with lines. These
lines map out the magnetic field and are called
magnetic field lines. The closer together
the lines, the stronger the field.
6. What makes something magnetic?
Domains…small areas where the groups of atoms are
aligned in the same direction. This makes something
magnetic!
Magnetic Force
• A push or pull on an object that is caused
by a magnet;
• The magnetic force is stronger in large
magnets
Electricity and Magnetism – how
are they related?
A coil of wire carrying an electric current can
create a magnetic field! This is called a solenoid!
What is an electromagnet?
When an electric current is passed through a coil of wire
wrapped around a metal core, a very strong magnetic
field is produced. This is called an electromagnet.
What are electric motors?
An electric motor is a device which changes electrical
energy into mechanical energy.
How does an electric motor work?
Go to the next slide 
Simple as that!!
If an electric field can create a magnetic field, do you
think a magnetic field can create an electric field?
YES!
Moving a loop of wire through a magnetic field produces
an electric current. This is called electromagnetic
induction.
A generator is used to convert
mechanical energy into electrical energy by
electromagnetic induction.
Carefully study the next diagram:
Direct current versus alternating current –
AC vs DC : What’s the difference?
Direct current is electrical current which comes from a
battery which supplies a constant flow of electricity in
one direction.
Alternating current is electrical current which comes
from a generator. As the electromagnet is rotated in the
permanent magnet the direction of the current alternates
once for every revolution.
Go to this website and click the button for DC then for
AC to visually see the difference between the two.
You can see that the DC source is a battery – current
flows in one direction. The AC source is the generator
and the current alternates once for each revolution.